DESCRIPTION (Adapted from Applicant's Description): Impaired manual dexterity is often one of the most disabling motor symptoms of Huntington's disease (HD). The neural mechanisms underlying the impaired hand function are poorly understood. The investigators propose to address this issue by examining the fingertip forces employed during manipulation of an object between the thumb and index finger (precision grip). Patients with HD will be asked to grasp and lift a custom made instrument (whose weight will be varied) using the precision grip, while the grip (pinch) and vertical lift force will be measured with strain gauge transducers. Furthermore, kinematics of the hand will be recorded using an optoelectronic device. Both temporal and force amplitude measures will be compared to age-matched control subjects to determine whether impaired hand function in HD is attributed to problems with movement sequencing, anticipatory and sensory control of prehensile forces, and/or chorea intruding upon the hand motor function. The specific aims are: #1. To test the hypothesis that patients with HD have prolonged transitions between movement phases and an uncoupling of the normal parallel generation of grip and lift force during object manipulation. #2. To test the hypothesis that these patients are impaired in their ability to scale (plan) the fingertip force output based on predicted physical properties (e.g., weight) of the object. #3. To test the hypothesis that patients with HD are impaired in their ability to use sensory information to adapt the grip forces to the object's weight, and will use excessive forces to compensate for choreic movements. The investigators long-term objective is to understand the neural basis of hand impairment in HD in order to facilitate the development of therapeutic intervention.